1. Field of the Invention
The present invention relates to a detector supporting mechanism and, more particularly, to a detector supporting mechanism for supporting a detector which is used, for example, in a circularity measuring apparatus to detect a small displacement of a workpiece.
2. Related Art
A workpiece having a cylindrical shape is rotated about its axis and the circularity, the cylindricity or the like of the workpiece is measured. For example, a workpiece W shown as a workpiece with a flange in FIG. 12 is rotated about a rotational centerline WC, and the circularity of an outer peripheral portion of the cylinder is measured by bringing a probe P of a lever-type detector 31 or the like into contact with the outer peripheral portion of the cylinder and by detecting a runout of the outer peripheral portion. Alternatively, the circularity of a bore is measured by bringing the probe P of the detector 31 into contact with an inner peripheral portion of the bore, or a runout of the flange is detected by bringing the probe P into contact with the upper surface of the flange.
In this case, there is a need to perform detection and measurement in such a manner that, for example, a runout of the outer peripheral portion of the cylinder is detected in a state where the detector 31 is supported in a vertical attitude and where the detection direction is horizontally set, and a runout of the flange is thereafter detected by changing the attitude of the detector 31 to a horizontal position and by adjusting the detection direction to a vertical direction.
Various detector supporting mechanisms designed to facilitate change of the detection direction of the detector 31 have been proposed and circularity measuring apparatuses having such detector supporting mechanisms have also been proposed (see, for example, Japanese Patent Application Laid Open Nos. 11-063971, 07-091949, and 06-300505).
A detector supporting mechanism disclosed in Japanese Patent Application Laid Open No. 11-063971 is as shown in FIGS. 13 and 14. That is, one end of an L-shaped supporting arm 111 is rotatably mounted on a mount by means of a horizontal/vertical fine adjustment mechanism 22, and a detector 31 is fixed to the other end of the supporting arm 111. The supporting arm 111 is turned through an angle of 90° from a state in which the detector 31 is vertically supported (FIG. 13) to change the attitude of the detector 31 to a horizontal direction shown in FIG. 14.
In this case, the detection direction is still horizontal even after the supporting arm 111 has been turned through an angle of 90° to change the attitude of the detector 31 to the horizontal direction. To change the detection direction to the vertical direction, the detector 31 is rotated through an angle of 90° about its axis.
A detector supporting mechanism disclosed in Japanese Patent Application Laid Open No. 07-091949 is constructed so that, as shown in FIG. 15, a second arm 212 on which a detector 31 is supported is turned relative to a first arm 211 fixed on a mount 21 through an angle of 180° about a rotation axis RC inclined at an angle of 45° in one direction from the vertical direction.
In this case, the detection direction of the probe P when the detector 31 is in the vertical attitude corresponds to the direction of arrow H shown in the figure (the direction perpendicular to the plane of projection of the figure). The detection direction is still the same as the direction of arrow H in the figure even after the second arm 212 has been turned through an angle of 180° to change the attitude of the detector 31 to the horizontal as indicated by the double-dot dash line in the figure. To change the detection direction to the vertical direction (the direction of arrow V in the figure), the detector 31 is rotated through an angle of 90° about its axis KC.
A detector supporting mechanism disclosed in Japanese Patent Application Laid Open No. 06-300505 has a structure such as shown in FIGS. 16A and 16B. That is, a rotation axis RC inclined at an angle of 45° from the vertical direction on the movement axis HC side of a mount 21 is provided a first arm 311 fixed on the mount 21 at the other end, and a second arm 312 on which a detector 31 is supported is rotatable about the rotation axis RC.
As shown in FIG. 16A, a lever 31a of the detector 31 supported in a horizontal attitude is bent through an angle of 90° from the main body of the detector and a runout of an outer peripheral portion of a workpiece W is detected by means of a probe P at the tip. The second arm 312 is turned through an angle of 180° to enable detection of a runout of the upper surface of a flange of the workpiece W as shown in FIG. 16B. In this case, there is no need to rotate the detector 31 about the axis KC.